This proposal is a continuation of an epidemiologic study of HIV among intravenous drug users (IVDUs) . This study would extend to 8 years the follow-up of a cohort of 765 IVDUs to continue the investigation of 3 important epidemiologic questions (AIM 1) and to initiate the study of health services utilization and medical charges incurred by HIV negative & HIV positive IVDUs (AIMS 2-5): AIM 1a: Estimate the change in incidence of the presence of antibodies to HIV among IVDUs who initially screen negative; AIM 1b: Estimate mortality rates for seropositive and seronegative IVDUs and ascertain cause of death; AIM 1c: Conduct survival analyses to estimate relative survival and determine prognostic factors that relate to survival and death. AIM 2: Determine the use of all types of medical care services by seronegative and seropositive IVDUs. AIM 3: Determine the charges for all types of medical care services utilized by seronegative and seropositive IVDUs. AIM 4: Determine the status and type of insurance coverage of cohort members, the patterns of change in coverage over time, the predictors of these changes, and the association between insurance coverage and the receipt of care. AIM 5: Describe factors that affect patterns of health care utilization. To accomplish Aims 1a-c, the cohort will be followed 4 additional years at 6 month intervals. To accomplish Aims 2-5, a "nested" sample of the cohort will be supplemented with a sample of HIV positive IVDUs from an AIDS risk reduction program to create a pooled, stratified sample of 100 seronegative and 200 seropositive (100 asymptomatic, 100 symptomatic) IVDUs who will be followed at 6 month intervals for 4 years. To accomplish Aim 5, an ethnography of health services utilization will study 20 HIV-positive and 20 HIV negative IVDUs.